In recent years, display devices have been used in various apparatus as information display means for viewers. A new display panel (a major part of a display device, excluding an external circuit, a casing, and the like) that utilizes liquid crystal, plasma, electro-luminescence, field emission, or the like, becomes the mainstream of typical display devices now, in place of a Braun tube that was popularly utilized for display devices before. The new display panel generally has a flat display area in which a plurality of pixels, each being a basic unit for image formation in the display area, is arranged in a matrix, and is a type of display panel that enables the display device to be small in thickness. Hence, the new display device is also called “flat panel display” as a generic term.
Taking as an example an active-matrix liquid-crystal display device, which is a most typical display device now, a plurality of display areas are formed on a mother substrate made of an insulative material such as transparent glass or plastic. In each display area, pluralities of scan wirings and signal wirings are arranged in matrix patterns, and at their intersection points, thin film transistors, i.e., switching elements and pixels having pixel electrodes are arranged in a matrix. Through steps of forming them, the mother substrate is fabricated into an array substrate with the scan wirings, the signal wirings, the pixel electrodes, and various other wirings, terminals, and the likes formed thereon. The array substrate and its opposite substrate are bonded together with a gap of several μm, and cut and separated on a display area basis, thereby to obtain a plurality of liquid crystal panels (display panels). The gap is filled with a liquid crystal material. In addition, there are two methods of filling a liquid crystal: one is a one-drop fill method that is applied before an opposite substrate is bonded; and the other is a vacuum injection method that is applied after bonded.
In manufacturing steps prior to those of cutting and separating the array substrate and mounting a driver circuit and an external circuit, there has been a discharge breakdown problem that a short circuit or a break occurs in a scan wiring or a signal wiring formed on the array substrate owing to an external static electricity, or there has been a discharge breakdown problem of a gate insulation film that causes a change in characteristic such as a threshold level of the thin film transistor.
As a way to solve the above-mentioned problem, a configuration has been disclosed in, for example, JP Unexamined Patent Publication No. H11-119246A, in which an anti-static short wiring (short ring) that is commonly connected with plural scan-wiring leads and signal-wiring leads is provided in the vicinity of a cutting line along which the array substrate is to be cut into individual liquid crystal panels. The common connection with the scan wirings and the signal wirings, even if static electricity happens to occur therein, discharges its charge to diminish the potential difference between the wirings, which brings about an effect that a discharge breakdown is less likely to occur between the wirings.
As a rule, the short-wiring-formed area is disposed off, when the mother substrate is cut and separated into the plurality of display panels.
However, from the viewpoint of cost reduction of the display device, it is desirable to obtain the display panels as many as possible from one mother substrate. The short-wiring formed area to be disposed off are, as a matter of course, unusable for the display panel, which has caused a problem of reducing the number of display panels obtained from one mother substrate.
Moreover, if connection wirings that connect scan-wiring leads or signal-wiring leads to a short wiring are formed from the same layer for the scan wirings or the signal wirings by being directly extended from external-connection terminals for the scan wirings or the signal wirings, the connection wirings are usually located to intersect the cutting line along which the display panels are to be cut and separated from their mother substrate. As a result, the layer of the scan wirings or the signal wirings, i.e., the connection wiring layer is exposed on the cut end.
While scan wirings or signal wirings are generally formed of a metal film of low ohmic resistance, the low resistance metal film is likely to corrode under high temperature and high humidity environment. For this reason, if the connection wirings are formed of such a low resistance metal film, corrosion occurs, depending upon a use environment of the display device, beginning from the connection wirings exposed on the cut end, and gradually progresses to the external-connection terminals of the array substrate and further to the leads, resulting in a reliability problem such as a malfunction due to a break in a wiring during operation of the display device.